This invention relates to acousto-optic interaction devices, and is more particularly concerned with a novel multi-channel acoustic transducer electrode structure for bulk wave acousto-optic devices.
Bulk wave acousto-optic devices are generally well known. Broadly speaking, these devices typically comprise a body of acousto-optic material having a transducer mounted thereon for generating acoustic waves within the body. When a light beam, such as from a laser, is directed through the device at an appropriate angle of incidence, the beam is diffracted by the device. The path of the diffracted beam can be controlled by varying the acoustic frequency.
In practice, an incident light beam nearly always passes through the near field (the so-called "Fresnel zone") of the transducer. Because of the complex characteristics of the acoustic field within the Fresnel zone, a light beam may encounter different numbers of peaks and valleys in the field depending on the position of its path of travel beneath the transducer. The overall diffraction effect of these peaks and valleys (i.e., the Integrated Optical Effect) on an incident beam can vary significantly with location beneath the transducer. This variation in Integrated Optical Effect impairs the smoothness of the diffracted output beam and is deleterious in many (if not most) acousto-optic applications.
Cook et al have shown that by proper shaping of the transducer electrode, the Integrated Optical Effect on an incident beam in the Fresnel zone will be substantially the same regardless of the position of the beam under the electrode, thereby providing a smooth output beam. See Cook, Cavanaugh, and Dardy, "A Numerical Procedure For Calculating The Integrated Acoustooptic Effect," IEEE Transactions on Sonics and Ultrasonics, Vol. SU 27, No. 4, July, 1980. Cook et al further provided a method for calculating the Integrated Optical Effect for any individual electrode structure. Ibid. Applying this methodology it can readily be demonstrated that more than one electrode shape can yield the same Integrated Optical Effect. The present invention takes advantage of the foregoing factors in connection with multi-channel acousto-optic applications.
In multi-channel acousto-optic applications it is frequently desirable to control a plurality of uniform, overlapping diffracted beams at some image plane. Heretofore, there has been no simple and effective means for providing such output from a single bulk wave device. The incorporation of these devices in such multi-channel applications has thus tended to result in acousto-optic systems of considerable complexity. Current color separator systems, for example, may use as many as ten acousto-optic modulators to expose color film. The desired exposure is obtained by providing special means to combine the individual modulator output beams with the required degree of overlap in the film plane.
The present invention avoids such complexities and other disadvantages of the prior art.